Integrated devices and systems for performing temperature controlled reactions and analyses

ABSTRACT

Reactor systems that include a reaction receptacle that includes a plurality of reservoirs disposed in the surface of a substrate. The reactor system also typically includes a temperature control element having at least a first heat exchanger thermally coupled to it. The heat exchanger is, in turn, disposed within the at least one of the reservoirs whereby the heat exchanger transfers heat to or from a fluid disposed within the reservoir, which heat is conducted to or from the temperature control element.

BACKGROUND OF THE INVENTION

The biological and chemical sciences, much like the electronicsindustry, have sought to gain advantages of cost, speed and conveniencethrough miniaturization. The field of microfluidics has gainedsubstantial attention as a potential solution to the problems ofminiaturization in these areas, where fluid handling capabilities areoften the main barrier to substantial miniaturization.

For example, U.S. Pat. Nos. 5,304,487, 5,498,392, 5,635,358, 5,637,469and 5,726,026, all describe devices that include mesoscale flow systemsfor carrying out a large number of different types of chemical, andbiochemical reactions and analyses.

Published international patent application No. WO 96/04547 to Ramseydescribes microfluidic devices that incorporate electrokinetic means formoving fluids or other materials through interconnected microscalechannel networks. Such systems utilize electric fields applied along thelength of the various channels, typically via electrodes placed at thetermini of the channels, to controllably move materials through thechannels by one or both of electroosmosis and electrophoresis. Bymodulating the electric fields in intersecting channels, one caneffectively control the flow of material at intersections. This createsa combination pumping/valving system that requires no moving parts tofunction. The solid state nature of this material transport systemallows for simplicity of fabricating microfluidic devices, as well assimplified and more accurate control of fluid flow.

Published international patent application No. 98/00231 describes theuse of microfluidic systems in performing high throughput screening oflarge libraries of test compounds, e.g., pharmaceutical candidates,diagnostic samples, and the like. By performing these analysesmicrofluidically, one gains substantial advantages of throughput,reagent consumption, and automatability.

Another advantage of microfluidic systems is to provide the ability tointegrate large numbers of different operations in a single“lab-on-chip” device, for performing both upstream and downstreamprocessing of reactants for analysis and/or synthesis. For example,International Patent Application No. PCT/US98/17910, filed Aug. 27,1998, describes devices and systems that elegantly control and monitortemperature within microfluidic systems by applying electric currents tofluids to generate heat therein, as well as measure solutionconductivity as a measure of fluid temperature.

Despite the substantial advantages made in the field of microfluidics,improvements are always desirable which allow more simplisticintegration of analytical and synthetic operations. The presentinvention meets these and a variety of other needs.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a reactor system. Thereactor system comprises a reactor element with a plurality ofreservoirs disposed in a surface of a substrate, a heating element, andat least a first heat exchanger disposed within at least one of theplurality of reservoirs. The heat exchanger is in thermal communicationwith the heating element.

Another aspect of the present invention is a method of performingtemperature dependent reactions. The method comprises providing areactor system which is composed of a plurality of reservoirs disposedin a body structure. The reservoirs are fluidly connected to amicroscale channel network disposed in an interior portion of the bodystructure. A temperature control element, and a heat exchanger thermallycoupled with the temperature control element are also included. The heatexchanger is inserted into the reservoir. A first reactant is placedinto at least one of the reservoirs. The temperature within thereservoirs is controlled by modulating a temperature. The at least onereactant is transported from the at least first reservoir into themicroscale channel network.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1C schematically illustrate a temperature controlled reactorsystem of the present invention from a perspective view (FIG. 1A) and aside view (FIG. 1B). FIG. 1C illustrates the insertion of the heatexchanger portion of the system into the reservoirs of the reactionreceptacle.

FIG. 2 schematically illustrates an alternate embodiment of the systemsof the invention in which the heat exchangers also function aselectrodes for driving material transport in an interconnected channelstructure within the reaction receptacle.

FIG. 3 schematically illustrates a system similar to that shown in FIG.1, but employing heat exchanger arrays.

FIG. 4 shows the channel layout of a reaction receptacle/microfluidicdevice for carrying out temperature dependent reactions followed byanalysis of the products of that reaction.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides novel systems for carrying outintegrated reactions and analyses where those reactions and/or analysesrequire accurate temperature control. Further, by carrying out theseoperations in the microfluidic regime, such operations have increasedthroughput with decreased reagent requirements.

In a first aspect, the present invention provides a reactor system thatincludes a reaction receptacle that includes a plurality of reservoirsdisposed in the surface of a substrate. The reactor system alsotypically includes a temperature control element having at least a firstheat exchanger thermally coupled to it. The heat exchanger is, in turn,disposed within the at least one of the reservoirs whereby the heatexchanger transfers heat to or from a fluid disposed within thereservoir, which heat is conducted to or from the temperature controlelement.

As noted above, the reaction receptacle portion of the present inventiontypically includes a plurality of fluid reservoirs disposed in thesurface of a single substrate, in order to permit the performance of anumber of different reactions simultaneously, or over time, without theneed for a number of different receptacles. The reservoirs describedherein generally have relatively small volumes to permit very smallreaction volumes. For example, preferred reservoirs typically have afluid capacity of less than or equal to about 200 μl, generally, lessthan or equal to about 100 μl. In order to provide such volumes, thereservoirs are typically from about 1 mm to about 10 mm deep and betweenabout 0.2 mm and 10 mm in cross-section, e.g., diameter or on an edge.For example, in particularly preferred aspects, reservoirs are circularhaving a diameter of between about 0.2 mm and about 5 mm, and a depthbetween about 1 mm and about 10 mm.

The substrate in which the reservoirs are disposed is typically planarin structure and is fabricated from a material that is substantiallyinert with respect to the reactions being carried out in the reservoirs.Preferred substrate materials include, e.g., silica-based substrates,such as glass, quartz, fused silica, silicon, and the like, polymericsubstrates, e.g., polystyrene, polypropylene, acrylic polymers, e.g.,polymethylmethacrylate, polycarbonate, polytetrafluoroethylene,polyvinylchloride, polydimethylsiloxane, polysulfone, polystyrene,polymethylpentene, polypropylene, polyethylene, polyvinylidine fluoride,and acrylonitrile-butadiene-styrene copolymer.

Also as noted above, in preferred aspects, the reaction receptacle hasintegrated within it, the capability to carry out one or more additionalanalytical or other operations. This is carried out by the incorporationwithin the substrate/reaction receptacle of at least a firstmicrofluidic channel network linking one or more of the plurality ofreservoirs disposed in the substrate.

Typically, substrates containing both reservoirs and integrated channelnetworks are fabricated from at least two different substrate layers,where one layer includes a plurality of apertures disposed through itwhich correspond to the reservoirs when the substrate layers are matedtogether to form the assembled reaction receptacle. The channel networkis typically defined between the two substrate layers as a series ofgrooves either fabricated into a surface of one or both of the substratelayers, or is defined by an additional layer applied to or disposed uponthe surface of one or both of the substrate layers. When the substratelayers are mated together, the grooves fabricated into the surface aresealed to define a plurality of fluid conduits or channels. Thesechannels are positioned such that they will be in fluid communicationwith one or more of the apertures disposed through one or both of thesubstrate layers, when the substrate layers are mated together. In thefinished product, this results in a plurality of reservoirs disposed inthe surface of the assembled substrate, where the reservoirs are influid communication with the channel network disposed within theinterior of the assembled substrate.

Typically, the channel network may include any of a number of differentchannel geometries, depending upon the operation that is to be carriedout by the overall system. For example, published International PatentApplication No. WO 98/49548 describes microfluidic devices that includepreferred channel geometries for performing separation analysis ofmultiple samples along a single separation channel, by individuallytransporting those samples from separate, integrated reservoirs into theseparation channel, and electrophoresing the samples down that channel.Published International Patent Application No. WO 98/00231, on the otherhand describes channel geometries that are useful in performing highthroughput screening operations. Each of these published applications ishereby incorporated herein by reference.

In particularly preferred aspects, the channel networks include at leasttwo intersecting microscale channels disposed within the interior of thesubstrate. As used herein, the term “microscale” or “microfabricated”generally refers to structural elements or features of a device whichhave at least one fabricated dimension in the range of from about 0.1 μmto about 500 μm. Thus, a device referred to as being microfabricated ormicroscale will include at least one structural element or featurehaving such a dimension. When used to describe a fluidic element, suchas a passage, channel, chamber or conduit, the terms “microscale,”“microfabricated” or “microfluidic” generally refer to one or more fluidpassages, channels, chambers or conduits which have at least oneinternal cross-sectional dimension, e.g., depth, width, length,diameter, etc., that is less than 500 μm, and typically between about0.1 μm and about 500 μm. In the devices of the present invention, themicroscale channels or chambers preferably have at least onecross-sectional dimension between about 0.1 μm and 200 μm, morepreferably between about 0.1 μm and 100 μm, and often between about 0.1μm and 20 μm. Accordingly, the microfluidic devices or systems preparedin accordance with the present invention typically include at least onemicroscale channel, usually at least two intersecting microscalechannels, and often, three or more intersecting channels disposed withina single body structure. Channel intersections may exist in a number offormats, including cross intersections, “T” intersections, or any numberof other structures whereby two channels are in fluid communication.

The reactor systems described herein also typically include atemperature control element that is in thermal communication with thereservoirs and preferably, in thermal communication with fluid disposedwithin those reservoirs. As used herein, the phrase “within thermalcommunication” refers to a connection between the reservoirs andpreferably a fluid within the reservoirs, and the temperature controlelement, which allows for the efficient transfer of heat between thereservoirs (or fluid) and the temperature control element.

In simple embodiments, the temperature control element comprises aheating element, such as a resistive heater, which can be adjusted toany of a number of preselected temperatures above ambient temperature.Such simple heating elements are well known in the art, and are usefulin those reactions/operations that require or benefit from elevatedtemperatures, e.g., above ambient.

In certain aspects, however, additional temperature control isdesirable, e.g., where a reaction benefits from temperatures belowambient, or requires a number of different reaction temperatures overtime for optimal performance. For example, often, reactions may requirea varying temperature profile over time, to optimize for a number ofdifferent reactions during that time. Examples of these reactionsinclude thermal cycling reactions, e.g., for performing nucleic acidamplification reactions, and the like. In such cases, thermoelectrictemperature control elements, e.g., peltier heaters/coolers arepreferred as the temperature control elements.

In accordance with the present invention, one or more heat exchangersare is also used to translate a requisite level of heat between thereservoirs of the reaction receptacle and the temperature controlelement. In particular, one or more heat exchangers is typicallyprovided in thermal communication with the temperature control element,and positioned such that the heat exchanger is disposed in, or isinsertable into one or more of the reservoirs, either separately, orsimultaneously, so that the heat exchanger is also in thermalcommunication with a fluid in the reservoir(s).

Heat exchangers can comprise any of a variety of thermally conductivematerials, including thermally conductive metals, i.e., copper,aluminum, platinum, and the like. In particularly preferred aspects, theheat exchanger comprises a material that is substantially inert to theconditions of the reaction that is to be performed. As such, aluminum,copper, platinum and ceramic heat exchangers are typically preferred,but other efficient heat exchanging materials can also be used, such ashigh-carbon polymer materials.

The systems described herein, in addition to benefiting fromintegratability and automatability, also provide benefits in terms ofproviding for rapid adjustment of fluid temperatures. Specifically,because the reservoirs have relatively small volumes, e.g., 200 μl orless, and the heat exchangers have efficient thermal transfer propertiesas a result of their structures and materials, fluids within thereservoirs can be heated substantially faster than in systems employingexternal temperature control sources, e.g., test tubes placed in heatingblocks, water baths, thermal cyclers, and the like. In particular,typical heating systems require several minutes to heat materials to100° C., in standard test tubes, microfuge tubes and the like. Formicrofluidic devices and fluids contained in the reservoirs of suchdevices, one would expect similar, or even longer temperature transitiontimes. Specifically, where a the temperature of a microfluidic devicereservoir is controlled by placing the entire device on a heatingelement, the relatively large amount of substrate as compared to thereservoir volume makes changes in temperature for the reservoir muchslower.

The heat exchangers are generally coupled to a surface of thetemperature control element, and are shaped or configured so that atleast a portion of the heat exchanger fits within the typically narrowdimensions of the reservoirs. Thus, the portion of the heat exchangerthat inserts into the reservoir will typically comprise dimensions thatare similar to, but smaller than the dimensions of the reservoirs. Forexample, in the case of the preferred reservoir dimensions describedabove, it will be appreciated that the dimensions of the heat exchangerportions will be from about 0.1 to about 8 mm wide, and between about0.5 mm and 8 mm deep. As used herein, the dimensions provided for theportions of the heat exchangers denote the boundaries of the spaceoccupied by the heat exchanger portion, rather than providing anabsolute measure of the structure, mass or shape of the heat exchanger.For example, where a heat exchanger comprises, e.g., a lattice or coilof thermally conductive material, the boundary dimensions of thatlattice or coil fit within the above described criteria. One of thegoals of these structures is to provide rapid, uniform temperaturecontrol across the full volume of a particular reservoir.

In order to optimize thermal transfer between fluid placed into thereservoirs and the heat exchangers, and consequently, the temperaturecontrol element, the heat exchangers are typically provided with arelatively large surface areas. This is generally accomplished byproviding the heat exchanger with a structure that increases the surfacearea across which thermal transfer may occur. Such structures mayinclude heat exchangers that are open cylinders which insert into thefluid reservoir of the device and provide both inside and outsidesurfaces of the cylinder for thermal transfer. Optionally, the heatexchangers may include additional structural elements to enhance thermaltransfer, including, e.g., fins, spines, ribs or the like. Alternativestructures may also be employed which provide such enhanced surfaceareas, including, e.g., coiled structures and/or sintered structuresfabricated from thermally conductive materials, e.g., metals, ceramics,and thermally conductive polymers, as well as randomly formedstructures, e.g., crumpled wires, etc. All of these types of structureshave enhanced surface areas for thermal transfer.

In addition to there increased surface areas, these structures arereadily fabricated so that their boundaries are similar to, but slightlyless than the dimensions of the reservoirs into which they fit, asdescribed above. By dimensioning the heat exchangers in this way, onecan optimize temperature control within the reaction reservoir byminimizing the distance between any portion of the fluid and a portionof the heat exchanger, thereby minimizing temperature gradients throughthe reservoir. In microscale systems, this is particularly important asthe substrate in which the reservoirs are disposed will function as aheat sink, rapidly cooling fluid within the reservoirs, and particularlynear the walls of the reservoirs. Larger distances between the heatexchanger and the walls will result in more substantial temperaturegradients within the reservoirs, resulting in some fluids being eithertoo warm or too cool.

In the case of systems that include temperature control in multiplereservoirs, the heat exchanger portions of the overall system may befabricated separately and thermally linked to the temperature controlelement, e.g., as shown in FIGS. 1A-1C. However, in some preferredaspects, the heat exchanger portions that contact multiple differentreservoirs are part of a single heat exchanger array that is fabricatedas a single unit and thermally linked to the temperature control elementas a single unit. An example of an integrated heat exchanger array forcontrolling temperature in multiple reservoirs is shown in FIG. 3. Inparticular, the system 300, again includes the reaction receptacle 102having a plurality of reservoirs 104 disposed in its upper surface 106.In the system shown in FIG. 3, however, the thermal transfer structures312 that insert into each of several reservoirs contacting the fluidtherein, are attached to and preferably fabricated as a single componentwith each other as an array of heat exchangers 314. One or more of thesearrays 314 is then thermally coupled to the temperature control element108. Of course, the heat exchanger array can be configured to insertinto any number of reservoirs simultaneously. Further, in the case ofelectrokinetic material transport systems, arrays can be configured tocontact only a group of reservoirs that will be under the same appliedelectric fields for a given operation, again allowing their use aselectrodes. Specifically, where multiple electrodes are under the sameapplied electric potentials during the entire operation, they can alsobe bridged by a common heat exchanger/electrode.

In some cases, the desired reactions are performed as a prelude to anadditional analytical step. For example, often it is desirable tosubject reaction components to a subsequent analytical operation orreaction. For example, reaction products may be subjected to aseparation analysis to determine if a desired component was produced inthe reaction. Alternatively, reaction products may be combined withfurther reactants, which may have interfered with the previous step ofthe reaction. Accordingly, in preferred aspects, the reservoirs in whichthe desired reactions are carried out are disposed at termini of achannel network that is disposed within the substrate or body structure,as described above. Subsequent operations on a given sample may then beperformed at different locations within the reaction receptacle, e.g.,another reservoir or one or more channels coupled to the reservoirs, bytransporting the sample material from the reservoir to the otherlocation, through the interconnected channel network.

Movement of material from the reservoirs, through the channels can beaccomplished by a number of means, including, e.g., application ofpressure differentials and/or electric fields across channels, to drivematerial movement through those channels. Pressure differentials may beapplied across channels, by simply elevating or lowering the pressure atone terminus of a given channel relative to another terminus of thatchannel. For example, one can apply a vacuum at one end of a channel todraw fluid or other materials through that channel. Alternatively, onemay apply a positive pressure to a sample reservoir at one end of achannel to push that sample into and through the connected channel.Alternatively, microfabricated pumps and valves may be incorporated intothe channel network to drive and direct material movement.

In some preferred aspects, material is moved through the channels of thesystem through the controlled application of electric fields across thelengths of different channel segments. This type of material transportis referred to herein as “electrokinetic material transport.” As usedherein, “electrokinetic material transport systems” include systemswhich transport and direct materials within an interconnected channeland/or chamber containing structure, through the application ofelectrical fields to the materials, thereby causing material movementthrough and among the channel and/or chambers, i.e., cations will movetoward the negative electrode, while anions will move toward thepositive electrode.

Such electrokinetic material transport and direction systems includethose systems that rely upon the electrophoretic mobility of chargedspecies within the electric field applied to the structure. Such systemsare more particularly referred to as electrophoretic material transportsystems. Other electrokinetic material direction and transport systemsrely upon the electroosmotic flow of fluid and material within a channelor chamber structure which results from the application of an electricfield across such structures. In brief, when a fluid is placed into achannel which has a surface bearing charged functional groups, e.g.,hydroxyl groups in etched glass channels or glass microcapillaries,those groups can ionize. In the case of hydroxyl functional groups, thisionization, e.g., at neutral pH, results in the release of protons fromthe surface and into the fluid, creating a concentration of protons atnear the fluid/surface interface, or a positively charged sheathsurrounding the bulk fluid in the channel. Application of a voltagegradient across the length of the channel, will cause the proton sheathto move in the direction of the voltage drop, i.e., toward the negativeelectrode.

“Controlled electrokinetic material transport and direction,” as usedherein, refers to electrokinetic systems as described above, whichemploy active control of the voltages applied at multiple, i.e., morethan two, electrodes. Rephrased, such controlled electrokinetic systemsconcomitantly regulate voltage gradients applied across at least twointersecting channels. Controlled electrokinetic material transport isdescribed in Published PCT Application No. WO 96/04547, to Ramsey, whichis incorporated herein by reference in its entirety for all purposes. Inparticular, the preferred microfluidic devices and systems describedherein, include a body structure which includes at least twointersecting channels or fluid conduits, e.g., interconnected, enclosedchambers, which channels include at least three unintersected termini.The intersection of two channels refers to a point at which two or morechannels are in fluid communication with each other, and encompasses “T”intersections, cross intersections, “wagon wheel” intersections ofmultiple channels, or any other channel geometry where two or morechannels are in such fluid communication. An unintersected terminus of achannel is a point at which a channel terminates not as a result of thatchannel's intersection with another channel, e.g., a “T” intersection.In preferred aspects, the devices will include at least threeintersecting channels having at least four unintersected termini. In abasic cross channel structure, where a single horizontal channel isintersected and crossed by a single vertical channel, controlledelectrokinetic material transport operates to controllably directmaterial flow through the intersection, by providing constraining flowsfrom the other channels at the intersection. For example, assuming onewas desirous of transporting a first material through the horizontalchannel, e.g., from left to right, across the intersection with thevertical channel. Simple electrokinetic material flow of this materialacross the intersection could be accomplished by applying a voltagegradient across the length of the horizontal channel, i.e., applying afirst voltage to the left terminus of this channel, and a second, lowervoltage to the right terminus of this channel, or by allowing the rightterminus to float (applying no voltage). However, this type of materialflow through the intersection would result in a substantial amount ofdiffusion at the intersection, resulting from both the natural diffusiveproperties of the material being transported in the medium used, as wellas convective effects at the intersection.

In controlled electrokinetic material transport, the material beingtransported across the intersection is constrained by low level flowfrom the side channels, e.g., the top and bottom channels. This isaccomplished by applying a slight voltage gradient along the path ofmaterial flow, e.g., from the top or bottom termini of the verticalchannel, toward the right terminus. The result is a “pinching” of thematerial flow at the intersection, which prevents the diffusion of thematerial into the vertical channel. The pinched volume of material atthe intersection may then be injected into the vertical channel byapplying a voltage gradient across the length of the vertical channel,i.e., from the top terminus to the bottom terminus. In order to avoidany bleeding over of material from the horizontal channel during thisinjection, a low level of flow is directed back into the side channels,resulting in a “pull back” of the material from the intersection.

In addition to pinched injection schemes, controlled electrokineticmaterial transport is readily utilized to create virtual valves whichinclude no mechanical or moving parts. Specifically, with reference tothe cross intersection described above, flow of material from onechannel segment to another, e.g., the left arm to the right arm of thehorizontal channel, can be efficiently regulated, stopped andreinitiated, by a controlled flow from the vertical channel, e.g., fromthe bottom arm to the top arm of the vertical channel. Specifically, inthe ‘off’ mode, the material is transported from the left arm, throughthe intersection and into the top arm by applying a voltage gradientacross the left and top termini. A constraining flow is directed fromthe bottom arm to the top arm by applying a similar voltage gradientalong this path (from the bottom terminus to the top terminus). Meteredamounts of material are then dispensed from the left arm into the rightarm of the horizontal channel by switching the applied voltage gradientfrom left to top, to left to right. The amount of time and the voltagegradient applied dictates the amount of material that will be dispensedin this manner.

Although described for the purposes of illustration with respect to afour way, cross intersection, these controlled electrokinetic materialtransport systems can be readily adapted for more complex interconnectedchannel networks, e.g., arrays of interconnected parallel channels.

In the case of electrically driven material movement, it is generallypreferred to provide electrodes in contact with the channels of thedevice to deliver potential gradients across the length of the channels.This, in turn, is typically accomplished by placing electrodes intocontact with fluid disposed within the reservoirs at the termini ofthese channels.

In particularly preferred aspects, the heat exchangers are fabricatedfrom a material that is both thermally and electrically conductive, sothat they can function as both a heat exchanger and an electrode, whenplaced into a fluid filled reservoir. The electrodes/heat exchangers arethen separately and operably coupled to an electrical controller whichcontrols the application of electric potentials to the electrodes/heatexchangers to drive material movement through the channels in acontrolled manner. Coupling of the electrodes/heat exchangers to theelectrical controller is generally accomplished in a manner so as not tointerfere with he thermal transfer between the heat exchanger portionand the temperature control element. For example, electrical leads maybe patterned on the surface of the temperature control element and incontact with the heat exchanger/electrode. Alternatively, wires may bedisposed through the temperature control element to provide electricalcoupling between the electrodes/heat exchangers and the electricalcontroller.

In alternate aspects, electrodes may be separate from the heatexchangers and electrically connected to a reservoir via a separatefluid filled port and salt bridge configuration that is connected to thereservoir, e.g., as described in Published International Application No.WO 98/00231, which is incorporated herein by reference. In particular,the heat exchanger is inserted into a sample material containingreservoir, while the electrode is placed into an adjacent well that isionically linked to the sample reservoir via a salt bridge, or otherconnection having reduced fluid permeability.

One example of an overall reactor system in accordance with the presentinvention is illustrated in FIGS. 1A, 1B and 1C. As shown, the overallsystem 100 includes a reaction receptacle 102 that includes a pluralityof reservoirs 104 extending down from the upper surface 106 of thereceptacle 102. The system also includes a temperature control element108, which, as shown, comprises an electrically controlled temperaturecontrol element, e.g., a resistive heater or peltier device, that isoperably coupled to a temperature controller 110 which provides electriccurrent to the temperature control element 108 and optionally receivesfeedback signals, to change and control the temperature of element 108.The system further includes a plurality of heat exchangers 112, whichare in thermal communication with the temperature control element 108,and are positioned so that they can be inserted into separate reservoirs104 in the receptacle 102, to allow efficient thermal transfer betweenmaterial, e.g., fluid, in the reservoirs 104 and the temperature controlelement 108. A side view of these elements is shown in FIG. 1B. FIG. 1Cillustrates the insertion of the heat exchangers 112 into the reservoirs104.

Although illustrated as a plurality of separate heat exchangers, it willbe appreciated that the heat exchangers may be provided as arrays ofconnected heat exchangers where circumstances permit. For example, wherereservoirs need not be electrically or thermally isolated from oneanother, metallic heat exchanger arrays can be fabricated that extendsimultaneously into multiple reservoirs. Where it is desirable forreservoirs to be electrically isolated from one another, e.g., wherematerials are electrokinetically transported through a channel networkcoupled to the reservoirs, then individual heat exchangers arepreferred, but non electrically conductive heat exchanger arrays arealso useful.

FIG. 2A illustrates a side view of a system of the present invention inwhich the heat exchangers also function as electrodes to drive themovement of material within the system. In particular, as shown, thesystem 200 again includes a receptacle 202 which comprises a pluralityof reservoirs 204 extending from the upper surface 206 f the receptacle202. As shown, however, the receptacle 202 also includes a channelnetwork 216 disposed within the interior of the receptacle 202, andwhich connects the reservoirs 204 of the receptacle 202. FIG. 2Billustrates an exemplary receptacle 202 containing an integrated channelnetwork 216 from a perspective view.

The heat exchangers 212 are again in thermal communication with thetemperature control element 208, but are also in electricalcommunication with an electrical controller 220 which is capable ofdelivering varying voltages and/or currents to each of the separate heatexchangers causing them to function as heat exchangers/electrodes.Examples of electrical controllers for use in driving material movementare described in U.S. Pat. No. 5,800,690, which is incorporated hereinby reference. In optional aspects, a single electrical controller isused to control the application of current and/or voltage to each of theelectrodes, as well as providing the electrical current that controlsthe temperature control element.

Examples of such instruments are described in Published InternationalApplication No. WO 98/05424. Briefly, these instruments typicallyinclude a base unit, which optionally houses the control elements forthe instrument, e.g., electrical power supplies, optical detectionsystems, and the like. The base unit typically includes a nesting siteor well that is configured to receive the reactor element, e.g., themicrofluidic device. The base unit also typically includes an elementfor interfacing with the reactor element, e.g., a “reactor elementinterface component,” for imparting energy to the reactor element, e.g.,thermal, light, electrical energy or the like. In the case of thethermal control aspects of the present invention, the interfacecomponent typically includes at least one heat exchanger that is inthermal communication with a heating element, as described herein. Theheat exchanger is typically positioned or configured on the interfacecomponent such that it can be easily inserted into at least onereservoir of the reactor element thereby contacting a fluid disposedtherein. The interface element may comprise any number of optionalstructures, including, e.g., a clamshell structure which rotatablycloses over the nesting site and reactor element to bring the heatexchanger into contact with the fluid filled reservoir. Other suchstructures include, e.g., press-like structures which uniformly lowerover the nesting site, and will be readily apparent to one of ordinaryskill in the art upon reading this disclosure.

As noted previously, the devices and systems of the present inventionare typically employed where one wishes to perform a temperaturedependent reaction within a particularly limited volume, e.g., less than100 μl. These devices and systems are particularly useful where onefurther wishes to perform additional operations on the materials thatare subjected to the temperature dependent reactions. In one aspect, thedevices and systems of the invention are particularly suited forperforming integrated nucleic acid analyses which require a temperaturedependent reaction prior to an analysis step. For example, where onewishes to determine whether a given sample contains a nucleic acidsequence of interest, the sample is typically subjected to anamplification reaction to select and amplify the nucleic acid sequenceof interest, if present. This is generally followed by acharacterization of the amplified products by, e.g., an electrophoreticseparation and detection, or specific hybridization reaction, e.g., toan oligonucleotide array, to identify whether the nucleic acid ofinterest is present.

With reference to the microfluidic device/reaction receptacle shown inFIG. 4, and in the case of the systems of the present invention, thissimply requires the placement of the sample material into a reservoir ofthe device 400, e.g., reservoir 402. In addition to the samplematerials, appropriate amplification reagents are also typically addedto the reservoir, e.g., anti-parallel primers that are complementary tothe nucleic acid sequence of interest, nucleic acid polymerase enzyme,i.e. taq polymerase, klenow, etc., as well as appropriate buffers andsalts, e.g., MgCl₂. The reaction mixture is then subjected to anappropriate thermal cycling profile by virtue of the temperature controlelement and heat exchangers placed into the reservoirs to amplify thesequence of interest using for example the polymerase chain reaction(PCR). Specifically, the temperature control element heats the contentsof the reservoir to, e.g., 95° C., to melt apart double stranded nucleicacids. The mixture is then cooled to, e.g., 45° C., to allow annealingof the primer sequences to the template sequence of interest. Themixture is then heated to, e.g., 70-80° C., to allow the polymerase toextend the primer sequences along the template sequence of interest.This cycling is repeated a number of times, e.g., 30-50 times, resultingin a geometric production of copies of the sequence of interest.

Once the amplification reaction is complete, a portion of the amplifiedproduct is transported out of the reservoir 402 via channel 402 a, intoloading channel 434, and across the intersection 446 of channel 434 andchannel 444, into channel 436. As noted above, this material transportis accomplished by applying a gradient in the electrical potential alongthe path of desired material movement, e.g., by applying a currentbetween reservoir 402 and reservoir 430. Once the material has crossedthe intersection 446, the potential gradient is then applied alongchannel 444 to inject that portion of the material at the intersection446 into channel 444. Incorporation of an appropriate separation matrixcauses nucleic acids of different molecular weight to migrate atdifferent speeds, allowing their separation. Incorporation of afluorescent label into the amplified product during amplification, thenallows detection of that product. Because the reactionreceptacle/microfluidic device includes multiple reservoirs connected tothe channel network, e.g., reservoirs 402-424, multiple samples may beanalyzed in series. Specifically, thermal cycling is carried outsimultaneously in each of the different reservoirs 402-424. Followingamplification, each sample is, in turn, injected into the mainseparation channel 444 of the device, substantially as described above,for separation analysis. Further, while each sample is being analyzed,the next sample is preloaded up to a point adjacent to the injectionintersection 446. In particular, while the sample from reservoir 402 isseparating in channel 444, the next sample, e.g., from reservoir 410, istransported through channel 410 a into channel 434 and then into channel438, without crossing the separation channel 444. Once separation of thefirst sample is completed, the next sample, which is already to thepoint adjacent to the main channel is simply shunted across theintersection 446 and injected into the main separation channel. The useof this preload function is described in detail in PublishedInternational Patent Application No. WO 98/49548, previouslyincorporated herein by reference.

In a similar manner, the devices and systems described herein are alsoparticularly suited to a variety of other applications, including SDScapillary gel electrophoresis (SDS-CGE) for the characterization ofproteins and other polyamino acids. In particular, prior to analysis,protein samples typically require denaturatioin in the presence ofdetergent at elevated temperatures, e.g., 100° C. Use of the deviceshown in FIG. 4 for this application has been described in, e.g.,copending U.S. patent application Ser. No. 09/243,149, filed Feb. 2,1999, now abandoned, and incorporated herein by reference. In accordancewith the present invention, sample denaturation is readily carried outwithin the reservoirs of the receptacle/microfluidic device using thetemperature control systems described above. Sample denaturation is thenfollowed by an analytical separation within the main reaction channel444.

Additional reactions that are temperature dependent, e.g. requiringelevated or reduced temperatures are also generally performed using thesystems described herein.

All publications and patent applications are herein incorporated byreference to the same extent as if each individual publication or patentapplication was specifically and individually indicated to beincorporated by reference. Although the present invention has beendescribed in some detail by way of illustration and example for purposesof clarity, it will be apparent that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:
 1. A reactor system, comprising: a reactor elementcomprising a plurality of reservoirs disposed in a surface of asubstrate; a heating element; and at least a first heat exchangerdisposed within at least one of the plurality of reservoirs, the heatexchanger being in thermal communication with the heating element,wherein the heat exchanger comprises a plurality of fins.
 2. The reactorsystem of claim 1, wherein the heat exchanger is electrically conductiveand is operably coupled to an electrical power supply.
 3. The reactorsystem of claim 1, further comprising an array of a plurality of heatexchangers in thermal communication with the heating element, each ofthe plurality of heat exchangers disposed in a separate reservoir. 4.The reactor system of claim 1, wherein the at least first heat exchangeris disposed on a solid frame that is removably positioned over thereactor element to insert the heat exchanger into the at least one ofthe plurality of reservoirs.
 5. The reactor system of claim 4, whereinthe frame is rotatably positioned over reactor element to rotate theheat exchanger into and out of the at least one of the plurality ofreservoirs.
 6. The reactor system of claim 1, wherein each of theplurality of reservoirs is in fluid communication with a channel networkdisposed within an interior region of the reactor element.
 7. Thereactor system of claim 1, wherein the heating element further comprisesa cooling element.
 8. A reactor system, comprising: a reactor elementcomprising a plurality of reservoirs disposed in a surface of asubstrate; a heating element; and at least a first heat exchangerdisposed within at least one of the plurality of reservoirs, the heatexchanger being in thermal communication with the heating element,wherein the heat exchanger comprises a coil.
 9. The reactor system ofclaim 8, wherein the heat exchanger is electrically conductive and isoperably coupled to an electrical power supply.
 10. The reactor systemof claim 8, further comprising an array of a plurality of heatexchangers in thermal communication with the heating element, each ofthe plurality of heat exchangers disposed in a separate reservoir. 11.The reactor system of claim 8, wherein the at least first heat exchangeris disposed on a solid frame that is removably positioned over thereactor element to insert the heat exchanger into the at least one ofthe plurality of reservoirs.
 12. The reactor system of claim 11, whereinthe frame is rotatably positioned over reactor element to rotate theheat exchanger into and out of the at least one of the plurality ofreservoirs.
 13. The reactor system of claim 8, wherein each of theplurality of reservoirs is in fluid communication with a channel networkdisposed within an interior region of the reactor element.
 14. Thereactor system of claim 8, wherein the heating element further comprisesa cooling element.
 15. A reactor system, comprising: a reactor elementcomprising a plurality of reservoirs disposed in a surface of asubstrate; a heating element; and at least a first heat exchangerdisposed within at least one of the plurality of reservoirs, the heatexchanger being in thermal communication with the heating element,wherein the heat exchanger comprises a scintered metal element.
 16. Thereactor system of claim 15, wherein the heat exchanger is electricallyconductive and is operably coupled to an electrical power supply. 17.The reactor system of claim 15, further comprising an array of aplurality of heat exchangers in thermal communication with the heatingelement, each of the plurality of heat exchangers disposed in a separatereservoir.
 18. The reactor system of claim 15, wherein the at leastfirst heat exchanger is disposed on a solid frame that is removablypositioned over the reactor element to insert the heat exchanger intothe at least one of the plurality of reservoirs.
 19. The reactor systemof claim 18, wherein the frame is rotatably positioned over reactorelement to rotate the heat exchanger into and out of the at least one ofthe plurality of reservoirs.
 20. The reactor system of claim 15, whereineach of the plurality of reservoirs is in fluid communication with achannel network disposed within an interior region of the reactorelement.
 21. The reactor system of claim 15, wherein the heating elementfurther comprises a cooling element.
 22. A reactor system, comprising: areactor element comprising a plurality of reservoirs disposed in asurface of a substrate; a heating element; and at least a first heatexchanger disposed within at least one of the plurality of reservoirs,the heat exchanger being in thermal communication with the heatingelement, wherein the heat exchanger comprises a randomly compressedwire.
 23. The reactor system of claim 22, wherein the heat exchanger iselectrically conductive and is operably coupled to an electrical powersupply.
 24. The reactor system of claim 22, further comprising an arrayof a plurality of heat exchangers in thermal communication with theheating element, each of the plurality of heat exchangers disposed in aseparate reservoir.
 25. The reactor system of claim 22, wherein the atleast first heat exchanger is disposed on a solid frame that isremovably positioned over the reactor element to insert the heatexchanger into the at least one of the plurality of reservoirs.
 26. Thereactor system of claim 25, wherein the frame is rotatably positionedover reactor element to rotate the heat exchanger into and out of the atleast one of the plurality of reservoirs.
 27. The reactor system ofclaim 22, wherein each of the plurality of reservoirs is in fluidcommunication with a channel network disposed within an interior regionof the reactor element.
 28. The reactor system of claim 22, wherein theheating element further comprises a cooling element.